An adaptive signal-to-noise ratio estimator in mobile communication channels

Representing the reception condition directly, signal-to-noise ratio (SNR) is an important parameter in mobile propagation channels, and therefore is widely used in system performance evaluations and adaptive applications. Hence, this paper puts forward a frequency domain SNR estimator in mobile communications, where we exploit the signal model with the band-limited fading channel and the additive white Gaussian noise. With the above model, the noise power spectrum density can be estimated from the periodogram of channel-plus-noise signals, subsequently leading to our SNR estimation. Moreover, in order to degrade the intrinsic spectrum leakage of fast Fourier transform in periodogram calculation, the leakage expression is derived analytically and then an adaptive process is proposed to make a tradeoff between leakage reduction and noise smoothing. We verify our algorithm by simulations and observe high accuracy in a wide range of velocities and SNRs. Additionally, unlike the conventional work, the proposed estimator is not strictly based on the assumption of specific Doppler spectral shapes except for the requirement of the band-limited channel, hence it is robust to general mobile channels.     

Improved sensitivity analysis using a complex variable semi-analytical method

The semi-analytical method (SAM) is a computationally efficient and easy to implement approach often used for the sensitivity analysis of finite element models. However, it is known to exhibit serious inaccuracy for shape sensitivity analysis for structures modeled by beam, frame, plate, or shell elements. In the present paper, we use a semi-analytical approach based on complex variables (SACVM) to compute the sensitivity of finite element models composed of beam and plate elements. The SACVM combines the complex variable method (CVM) with the semi-analytical method (SAM) to obtain the response sensitivity accurately and efficiently. The current approach maintains the computational efficiency of the semi-analytical method but with higher accuracy. In addition, the current approach is insensitive to the choice of step size, a feature that simplifies its use in practical problems. The method is applicable to any structural elements including beam, frame, plate, or shell elements and only requires minor modifications to existing finite element codes.     

基于边缘信息C_V模型的医学图像分割方法

图像分割是医学处理中的重要研究内容之一,提出一种基于边缘信息的改进的C_V模型的医学图像分割方法.在模型中增加了表征边界特征的项,利用图像的边界信息与区域信息为分割服务,克服了传统C_V模型不能利用图像的梯度信息的不足.并对C_V模型的区域信息项进行了改造,改变了传统C_V模型中均值取值的定义,提高了对灰度层次丰富的图像分割能力.增加了距离函数惩罚项,将距离函数重新初始化的过程并入整个水平集框架模型中,极大地提高了曲线演化与分割速度.实验表明该模型是有效的医学图像分割方法.     

H∞ filtering of networked discrete-time systems with random packet losses

This paper studies the H_∞ filtering problem for networked discrete-time systems with random packet losses. The general multiple-input-multiple-output (MIMO) filtering system is considered. The multiple measurements are transmitted to the remote filter via distinct communication channels, and each measurement loss process is described by a two-state Markov chain. Both the mode-independent and the mode-dependent filters are considered, and the resulting filtering error system is modelled as a discrete-time Markovian system with multiple modes. A necessary and sufficient condition is derived for the filtering error system to be mean-square exponentially stable and achieve a prescribed H_∞ noise attenuation performance. The obtained condition implicitly establishes a relation between the packet loss probability and two parameters, namely, the exponential decay rate of the filtering error system and the H_∞ noise attenuation level. A convex optimization problem is formulated to design the desired filters with minimized H_∞ noise attenuation level bound. Finally, an illustrative example is given to show the effectiveness of the proposed results.     

椭圆曲线密码体制在WSN上的应用

分析椭圆曲线等公钥技术在无线传感器网络中的应用。介绍无线传感器网络操作系统TinyOS的体系结构、NesC程序开发基本流程和基于TinyOS的椭圆曲线密码库TinyECC。利用TinyECC设计并实现基于椭圆曲线密码体制的轻量级节点验证协议。分析结果证明该协议在无线传感器网络上可行。     

纹理去除的皮革图像颜色分类方法

针对皮革图像存在 天然纹理,凸凹结构纹理会使得扫描或摄影的皮革图像亮度变化明显,影响皮革图像颜色的准确分类,提出一种去除图像纹理的皮革图像颜色分类方法。首先利用相对总变差模型去除皮革图像纹理,获得只包含皮革图像颜色信息的图像;然后利用均匀彩色空间模型L*a*b*具有的较强的色差分辨能力,提取去除纹理后的皮革图像L*a*b*颜色分量的平均值作为皮革图像的整体的颜色特征;最后运用SVM支持向量机对皮革图像颜色特征进行分类。实验结果表明,该方法能够比较精确地区分皮革图像颜色,实现皮革图像的颜色分类,具有可行性 。     

语音信号特征参数研究

在语音技术的发展过程中使用了大量的语音信号特征参数,好的语音信号特征参数能对语音识别起至关重要的作用。本文对语音信号特征参数、语音信号特征参数的选择进行了介绍,并介绍了语音信号的短时能量、短时平均幅度的提取。     

Integral-inequality approach to delay-dependent robust H-infinity control for uncertain neutral systems

This paper focuses on the design problem of a memoryless state feedback robust H-infinity controller for a class of uncertain neutral systems. By using a newly established integral inequality, a new delay-dependent bounded real lemma for such systems is derived without involving a fixed model transformation. Furthermore, new delay-dependent sufficient conditions for the existence of robust H-infinity controllers are presented in terms of nonlinear matrix inequalities. A design procedure involving an iterative algorithm is also proposed to design such controllers. Numerical examples are given to demonstrate the less conservatism of the proposed method.     

基于四波混频的100Gbit/s全光逻辑异或门

该文利用高非线性光纤的非简并四波混频效应实现高速全光逻辑异或门.由于非简并四波混频过程中输出和输入光信号的复振幅是线性关系,因此,产生的闲频光携带了两束载波抑制归零差分相移键控调制格式的信号光的全光逻辑异或信息.通过数值模拟仿真,实现了100Gbit/s的全光逻辑异或门,并分析了信号光功率和探测光波长对全光逻辑异或门性能的影响.     

Raney-Ni催化下菜籽油生物柴油催化转移加氢的研究

在水环境下,以异丙醇为供氢体和Raney-Ni为催化剂,对菜籽油经酯交换得到的生物柴油进行催化转移加氢研究.通过定时取样分析生物柴油的碘值变化和组分含量,研究了生物柴油中亚麻酸甲酯(C18∶3)、亚油酸甲酯(C18∶2)和油酸甲酯(C18∶1)催化转移加氢选择性和反应动力学,以及加氢过程中不饱和脂肪酸甲酯的顺反异构情况.结果表明:在水环境下生物柴油催化转移加氢反应可用拟一级动力学模型来描述;C18∶3和C18∶2的加氢选择性较高,反应速率常数是C18∶1的6倍,但产物主要为反式油酸甲酯(t-C18∶1),而且顺式油酸甲酯(c-C18∶1)进一步加氢变成硬脂酸甲酯(C18∶0)的速率远远高于t-C18∶1.